The tremendous impacts involved in the operation of forging hammers can cause problems, the seriousness of which increases in accordance with the size of the hammer. With little or no vibration isolation, the impacts of large forging hammers can sometimes be felt over a mile away from the location of the hammers. Often, the shock of an improperly or unisolated forging hammer can crack building walls, damage other equipment in and around the facility where the hammer is located, creates an environmental nuisance, affects the accuracy of precision tools and instruments located at even substantial distances away and can actually pound the foundation on which the hammer is located down into the ground, making necessary frequent releveling.
Effective shock and vibration control systems for forging hammers have been known and widely used for many years. A good system will completely eliminate the transmission of shock between the hammer and the foundation and will, therefore, eliminate all of the problems referred to above. Moreover, a good shock and vibration system will make the operation of the hammer quieter and actually increase the efficiency of the hammer.
In some shock and vibration control systems proposed and used in the past, the vibration isolators and damping systems have often been installed outside of the perimeter of the inertia block to facilitate installation and maintenance of the isolators and dampers. In many installations, the isolators are of a type in which the top plate is connected by a screw to a beam constructed into the inertia block. This type of isolator can be installed in unloaded condition and loaded by threading the screw to lift the inertia block off the foundation. In a system that has apparently been used in Europe, isolators constructed in a manner that permits them to be preloaded prior to installation under the inertia block and then partially unloaded by loosening the preloading bolts have been employed.
The damping systems that have been used in shock and vibration control systems for forging hammers have been of the type that inherently produce forces of magnitudes that vary in the course of operation of the system. One type of damping employs a mechanical snubber similar to snubbers used in the couplings between railway cars. The construction of such mechanical snubbers is such that the forces that they produce increase as a function of the extent of compression, and mechanical snubbers are subject to failure under certain conditions, for example, because of the buildup of an excessive vertical or horizontal force. Hydraulic-type snubbers have also been used, but it is well known that the seals required to contain hydraulic fluid frequently fail and require excessive maintenance and result in costly shutdown time. Moreover, the force output of hydraulic-type dampers is dependent on the velocity of the vibrating equipment at any given point in time; accordingly, the damping forces are low just after impact of the hammer, increase to effective levels only after the load has developed some velocity, and then decrease as the load is decelerated toward the end of one-half cycle of vibration. Accordingly, hydraulic dampers work effectively only during part of each cycle of vibration, and from this point of view, hydraulic dampers are inefficient.
In recent years, the tendency has been toward the use of forging hammers of extremely large size and involving tremendous impact loads, and the greater size and consequent heavy static loads and, of course, the greater impact forces have increased the problems in providing effective shock and vibration control. The heavy loads and tremendous impacts involved require a very large number of isolators and highly reliable damping, particularly when the hammer is designed for relatively high production rates in terms of operations per minute. Vibration must be damped as rapidly as possible using highly reliable dampers. The heavy static loads of the equipment have increased the difficulties involved in construction and installation of the hammer and have, in some of the very large installations, made systems based on known technology extremely expensive.